1. Field of the Invention
The present invention relates to a resin composition for non-offsetting toners which are stable at low temperatures and are useful for xerographic printing methods.
2. Description of Related Arts
Typical image forming processes in xerographic methods and electrostatic printing methods include a development step, which includes uniformly charging a light-conducting insulation layer, exposing it to form an exposed portion, dispersing charges on the exposed portion to form an electric latent image, and applying charged fine toner powder to the latent image to visualize the image; an image transfer step, which includes transferring the visible image thus obtained onto a transfer material such as transfer paper; and a fixing step, which includes permanently fixing the transferred image onto the transfer material by heating or applying pressure. Therefore, toners and resins for toners must meet the various requirements therefor. More specifically, in the development step, toners and resins for toners must first retain a certain amount of charge with respect to an environment suitable for a copying machine, in order to apply the toner to the electric latent image (chargeability or electrifiability). Secondly, in the fixing step, toners have non-offsetting properties, that is, toners do not adhere to hot rolls in hot roll fixing methods, and at the same time have good fixing properties with respect to paper. Thirdly, toners must have anti-blocking properties, that is, toners retained in various devices such as copying machines and printers must not cause blocking.
Typical examples of resins conventionally used for toners include styrene/acrylic resins and polyesters. Toners containing styrene/acrylic resins are less susceptible to environmental effects when used and exhibit stable static properties (humidity resistance), but have poor fixing properties with respect to paper. On the other hand, toners containing polyesters have good fixing properties with respect to paper, but their humidity resistance is poor. When toners are adjusted so as to have good non-offsetting properties, one of the most important requirements for toners, both styrene/acrylic resins and polyesters exhibit poor fixing properties.
Under these circumstances, there is a keen demand for resins for toners which have the good performance of both styrene/acrylic resins and polyesters.
Heretofore, extensive investigations have been made into resins for toners containing both styrene/acrylic resins and polyesters, most of which investigations include the technique of mixing both types of materials with different SP values (solubility parameters) by uniformly dispersing them using an extruder, Bambury mixer or the like. However, it is difficult to obtain a resin having stable qualities exhibiting a stable mixed state, because both types of materials have not only different SP values but also different melt viscosities. Furthermore, conventional blends of copolymers or graft copolymers have poor humidity resistance, due to presence of a polyester component.
Therefore, there is still a keen demand for improved resins for toners.